data ccc;
  retain y;
  set aaa;
  if _N_ = 1 then set bbb;
run;

data步如何实现？

供参考：

/**方法1**/
data work.ccc1;
set work.aaa;
y="d";
run;


/**方法2**/
proc sql;
create table work.ccc2 as
select *
from work.aaa ,work.bbb;
quit;

data ccc;
  set aaa;
  retain y;
  if _N_ = 1 then set bbb;
run;

这样是不是更好！

是的，这样更好。